1. Field of the Invention
The present invention relates to a hard anti-abrasive layer and a tool coated with the anti-abrasive layer.
2. Discussion of the Background
Specialists in the field have endeavoured for some considerable time to find an anti-abrasive layer for dry working of metals. “Dry stationery working” or “dry working” means cutting without cooling liquid and lubricant but also cutting with minimum quantities of lubrication.
The development of the anti-abrasive layer, in particular the selection of the layer material, was based on the consideration that the tool reaches considerably higher temperatures during cutting and that this undesirable temperature increase can be reduced if as high a proportion of the heat as possible is removed not via the tool but via the chips obtained during the cutting. The possibility has therefore been considered of combining materials which had been known to possess either a high hot hardness and/or a high resistance to oxidation and/or a low thermal conductivity.
The most widely used anti-abrasion layer consists of a golden yellow titanium nitride TiN. TiN layers can be used universally. Layers of the dark bluish red iridescent titanium aluminium nitride (Ti,Al)N are known for their high hot hardness. Usually, they possess a percentage ratio of titanium to aluminium atoms of 50:50 or (Ti0.5, Al0.5)N, occasionally also displaced in the direction of 40:60 or ((Ti0.4, Al0.6)N. To improve the quality of tools, they are used both as individual layer (see e.g. Gilles et al, Surface and Coatings Technology 94-95 (1997) 285-290) as well as a (Tl,Al)N/TiN multiple layer with intermediate layers of titanium nitride (compare e.g. the so-called FIRE layer of Gühring oHG).
CrN layers are recommended for working non-iron metals (see e.g. P. Hones, Surface and Coatings Technology 94-95 (1997) 398-402).
MeCrAlY alloys (Me=metal) are also known for coating turbine blades. They increase the resistance to oxidation and the thermal insulation and consequently the permissible temperature and the efficiency of aeroplane engines (see e.g. W. Brandl et al, Surface and Coatings Technology 94-95 (1997) 21-26).
Recently, a multilayer of (Ti,Al)N and CrN has become known (see e.g. I. Wadsworth et al, Surface and Coatings Technology 94-95 (1997) 315-321). Its resistance to oxidation increased with the proportion of Cr, at least up to proportions of Cr of 30 at %. In the same laboratory, layers of TiAlN with small admixtures of Cr and Y have also been examined (see DE 19818782, filed Apr. 27, 1998).